MinJ is a conserved nine-pass transmembrane protein that contains a putative transmembrane β-sheet

The Min system disassembles FtsZ-rings after septation in Bacillus subtilis and is localized to the nascent division plane and cell poles by the protein MinJ. The N-terminal region of MinJ contains transmembrane segments while the C-terminal region of MinJ contains a PDZ domain but its topology and functional domains are poorly understood. Here we empirically test MinJ topology based on a variety of transmembrane prediction models and find that the data is most consistent with Alphafold3, which predicts a 9-pass transmembrane protein with an external N-terminus and internal C-terminus. Deletion analysis indicates that all regions of the protein tested are required for function but deletion of the PDZ domain alone preserves polar localization and interaction with both MinD and DivIVA. Moreover, Alphafold predicts that transmembrane segments 6 and 7 comprise staves of an unusual transmembrane {beta}-sheet and deletion of the putative {beta}-sheet in the absence of MinD results in a minicell frequency that exceeds mutation of MinD alone. Bioinformatic analysis indicates that MinJ is highly conserved within Firmicutes and is co-conserved with MinD and DivIVA with which it interacts. Our data clarify the structure of MinJ and support models in which MinJ has functions in addition to restricting the activity of the Min system.